It has long been known that forward biased p-n junctions in certain compound semiconductor materials will emit light. Semiconductor p-n junction diodes have been arranged in arrays to provide alphanumeric, character, or seven segment displays. Such arrays as previously produced were relatively expensive since they involved producing the diode junction structure on a large slice of material which was thereafter cut or broken into a large number of individual diodes, thus electrically isolating them from each other, and then reassembling the diodes into arrays for arrangements to provide the characters desired. Finally, individual wire connections had to be accomplished to at least one electrode of each diode. Further, planar processing is complicated, and the resulting planar geometry is not optimum for emitting light because of internal reflection. Element nonuniformity, misalignment and bad connections cause a high percentage of rework or rejection in conventional light emitting diodes (LEDs). This fact, coupled with the labor intensive nature of the process involved as well as its inherently high rated material waste, made LED displays relatively expensive to produce, and made it difficult to fabricate large displays having good resolution (a high number of lighted points per unit area).
Other displays, such as liquid crystal displays and electrochromic displays, typically require ambient light to be visible, and are likely to have problems as to service life-time and to be temperature sensitive. Electroluminescent displays require high voltage as do plasma displays.
To overcome the weaknesses of the conventional LED display, a light emitting diode taking the form of a sphere or spheroid has been used. In pending U.S. Application Ser. No. 752,389 filed Dec. 20, 1976 and entitled "Light Emitting Diode Element in Character Display" by G. F. Wakefield, a spherical light emitting element having a multilayer sphere of different materials forming a subsurface p-n junction inserted into an insulation member is disclosed.